2013 is a year of optimism in Miami. It's a year of hope after a 2012 Dolphins squad led by an inexperienced rookie quarterback went 7-9, and were in the thick of the AFC playoff race through Week 16, despite a 1-5 midseason stretch, and difficult losses in games that could have been won.

Now, the Dolphins are coming back a year later after the most active free agency of any NFL team, having signed such players as Mike Wallace and DannellEllerbe.

With the Dolphins having made the playoffs just once in the past 10 years, fans in South Florida obviously don't want to get their hopes up—they've seen this storyline before.

Yes, the attention and pressure will be on Tannehill, the first-round pick of the Dolphins from last year.

But one player who will be key to this season, will be none other than the fourth-round pick from that same draft—running back Lamar Miller.

The Background

Reggie Bush spent two seasons in a Dolphins uniform, and actually had a solid stay in South Florida.

2011 was his best year, and saw him eclipse the 1,000-yard mark during the season on the ground for the first time in his career while averaging a remarkable 5.0 yards per carry. The Dolphins finished the season ranked 11th in the NFL running the football.

A season later, Bush eclipsed the 1,000-yard mark again, but his yards per carry dipped down to 4.3, while the Miami rushing attack fell down the charts, ranking 17th last season.

Simple background—Bush had a productive two-year stay in Miami, but the Dolphins allowed Bush to walk as a free agent, opening up a starting running back competition that will take place until the regular season starts.

Per Adam Beasley of The Sun Sentinel, Coach Joe Philbin commented on why Miami was ready to move on from Bush:

We liked the guys we had. We thought there was potential there. We thought there was opportunity for growth and development out of those guys, and we’ll see how that goes here in the next couple weeks and months.

Miller is a back who relies mainly on his speed, but hits holes with aggression—unlike his predecessor Bush—and mixes in a little bit of power running when needed.

Bucky Brooks of NFL.com, while profiling the Dolphins, claimed that "Lamar Miller is the NFL's best-kept secret."

I believe Miller is a Clinton Portis clone, with the tools to be a dominant runner in the NFL. He has the speed to turn the corner on outside runs, while also displaying the toughness to pick up the hard yards between the tackles. Additionally, he possesses the elusiveness to make defenders miss in the open field on the way to big gains.

Brooks goes on to note Miller's stop-start quickness, and how Miami's willingness to use more three-receiver formations in 2013 will show off Miller's all-around talents.

Miller's Weaknesses

One major reason why Miller was sporadically used during the course of his rookie season—he carried the ball just 51 times—was his inability to pass block.

This is the reason why despite Thomas's lack of explosive running ability—he's averaged just 3.5 yards a carry through two seasons—he was on the field more than the rookie Miller. The Kansas State product finished with 91 carries on the year as the primary backup to Bush.

That might not be a problem in 2013.

Earlier this month, Coach Joe Philbinprasied Miller's improvements as a pass blocker. Quarterback Ryan Tannehill recently backed up those claims, via Barry Jackson of The Miami Herald: "He’s picking up pass protections a lot better. Now that he’s got that, he’s going to be a great player.”

If pass blocking won't hold back the University of Miami product as it did during his rookie season, the Dolphins won't take him off of the field for pivotal third-down conversions as they did in 2012.

2013 Outlook

This is Miller's job. Despite Thomas's second-round selection from two years prior, it's evident he doesn't have the burst and ability needed at the pro level to be a true starting running back. He is best served to gain yards in short-yardage situations utilizing his big 230-pound frame, while also being used in versatile roles as a pass blocker.

Miller has the attributes—speed and big-play ability—to become a true home-run threat in Miami's backfield.

Brooks was not far off when he called Miller "the NFL's best kept secret." This is the next breakthrough running back of the NFL.

Barring a catastrophic injury, Miller should emerge as one of the better running backs in the NFL in 2013.